(1) Field of the Invention
The present invention relates to a process for the preparation of synthetic fibers. More particularly, the present invention relates to a process for the preparation of synthetic fibers, in which a fiber bundle of a number of single filaments, especially monofilaments, arranged in parallel to one another can be spun from a single orifice or nozzle. According to the present invention, such fibers can be prepared even from low density polyethylene and an ethylene/vinyl acetate copolymer.
(2) Description of the Prior Art
Various techniques have heretofore been proposed in connection with ultra-fine filament bundles having a diameter smaller than several hundred microns and processes for the preparation thereof. For example, there can be mentioned a process in which ultra-fine filaments are prepared by the super-draw method (Japanese Patent Publication No. 617/53), the flash spinning method (Japanese Patent Publication No. 11851/60) or the jet spinning method and many ultra-fine filaments are gathered by using a binder component or by mechanical twisting (in case of ultra-fine filaments, gathering by mechanical twisting substantially difficult). However, when the super-draw method is adopted, kinds of applicable resins are limited and since a special drawing step is necessary after spinning, the scale of the apparatus is increased and the structure becomes complicated. Although many resins are applicable to the flash spinning method, only short fibers are formed and it is difficult to obtain continuous filaments. Furthermore, since the solvent is scattered at the flashing step, the method is not preferred from the viewpoint of the safety or working environment. The jet spinning method is disadvantageous in that a spinneret having a special shape should be used, and this method involves the same problems as described with reference to the flash spinning method. Moreover, in each of these methods, secondary processing is necessary for preparing a fiber bundle, and this secondary processing is very difficult because the strength of the fiber is very low.
Accordingly, there has been proposed a polymer blend fiber dissolving process or arranged polymer fiber dissolving process in which a filament having an islands-in-sea structure is spun by using two kinds of resin components, an ultra-fine filament of the island component is left while extracting and removing the sea component and these ultra-fine filaments are gathered to form a fiber bundle. However, in most of known techniques of the polymer blend fiber dissolving process, the length of the island component in the longitudinal direction is short and hence, it is difficult to form continuous filaments. A trial to form continuous filaments is proposed in Japanese Patent Publication No. 21167/69, but in an ultra-fine filament bundle prepared according to this proposal, ultra-fine filaments are entangled in the net-like form and the arrangement of ultra-fine filaments is disturbed. In the latter-mentioned arranged polymer fiber dissolving process, since the island component is long and continuous in the longitudinal direction, a bundle of continuous ultra-fine filaments can be prepared and in the obtained fiber bundle, the constituent ultra-fine filaments are independently arranged in parallel to one another. However, since a spinneret having a special structure should be used, the apparatus becomes complicated and expensive. Moreover, in these processes, a bundle of ultra-fine filaments cannot be obtained unless the post treatment of extracting the sea component is carried out.